1. Technical Field of the Invention
The present invention relates to a pump control mechanism, a printer using the pump control mechanism and a pump control method.
2. Description of the Related Art
Many popular type printers are designed so that an ink-stored cartridge is mounted on a carriage. However, there is known such a high-performance type of printer that a cartridge is not mounted on a carriage, but a cartridge is mounted at the housing side of the printer. In this type of printer, the variation of the weight of the carriage can be suppressed even when the residual amount of ink is varied. Therefore, this type of printer can perform high-precision control on the movement of the carriage.
Here, in the above type of printer, a liquid container is mounted on a carriage. A cartridge is connected to the liquid container through a liquid pipe line so that ink can be supplied from the cartridge to the liquid container. Furthermore, the cartridge is connected to one end side of an air pipe line. The other end side of the air pipe line is connected to a bellows pump in a pump unit. By driving the bellows pump, air is fed through the air pipe line into the cartridge. Ink can be supplied from the cartridge through the liquid pipe line into the liquid container by air pressure.
JP-T-2002-510252 (see page 8, FIG. 1) discloses a construction using air pressure as described above. The construction disclosed in the Patent Document 1 is equipped with a reciprocating portion that is reciprocated to compress air, a pump motor for reciprocating the reciprocating portion and a power supply portion for supplying power to the pump motor until the pressure of the liquid container reaches a predetermined pressure.
When a bellows pump is driven by a pump motor, there occurs a problem that noise occurs from noise sources such as the pump motor, a conversion mechanism, etc. These noises out of operating sounds occurring from a printer are particularly large, and it has been required to reduce these noises.
Particularly when the bellows pump is expanded and contracted, the load acting on the pump motor is varied in accordance with variation of the internal pressure of the bellows pump, and the rotational number of the pump motor is also varied in accordance with the variation of the internal pressure concerned, so that the noise is also varied in accordance with the variation of the rotational number. When the noise is varied in accordance with the rotational number, the noise more easily jars unpleasantly on the ear as compared with a case where a sound having a fixed level statitionarily occurs from a noise source. That is, in the case of the same level noise, a sound varying in magnitude makes a human feel more noisy than a sound fixed in magnitude.
Here, when the above-described pump motor is controlled, for example by mounting a sensor that can detect the rotational number of a rotary encoder or the like and actively using a feedback signal from the sensor to control the rotational number of the pump motor, the noise can be reduced. However, when a rotary encoder or the like is mounted, there is a problem that it causes rise-up of the cost, etc. Therefore, it has been required that the noise can be reduced without using any rotary encoder by the detection of a position detecting sensor and a pressure sensor which has been already equipped to the pump unit.
Furthermore, when the bellows pump is driven, there also occurs a problem that the actual load acting on the pump motor is greatly varied in magnitude. Therefore, when a locally large load acts on the pump motor, the pump motor does not overcome the load concerned and thus the pump motor is stopped at that portion.
The stop problem described above is more remarkable as the use term of a printer is longer. That is, when the use term of the printer is increased, the influence of external disturbance factors such as degradation of the fabrication precision of mechanical parts, adhesion of dust from the outside, etc., which are not considered as design matters at the initial stage, is more intense. The influence of the external disturbance described above is frequently further applied to load-large parts which have hitherto existed.
For example, it is assumed that a mechanically jouncing part has existed from the initial stage of the Manufacturing of a printer, an impact load is caused by the jouncing and thus there exists a portion at which the load is locally increased. Accordingly, when the use term of the printer is increased, it is an usual case that the fabrication precision is generally degraded because of abrasion due to friction or the like, loose of screws or the like, and the impact load is further increased. In this case, there frequently occurs such a case that variation in magnitude of the load is further intensified and thus the pump motor is stopped. The problem that the variation width in magnitude of the load is increased as the printer is used for a longer term is also likewise caused by other elucidated factors/non-elucidated factors.
As described above, in addition to the promotion of quietness, it is necessary in the printer to prevent the pump motor from being stopped in process of its operation due to variation in magnitude of the load, and both of them are required to be compatibly satisfied. Here, in order to prevent the pump motor from being stopped in process of its operation, the voltage/current to be applied to the pump motor may be increased. However, in this case, the rotational speed of the pump motor is increased, and thus it is difficult to implement quietness in the pump unit.
On the other hand, the stop problem described above is apt to occur at a portion at which the pump motor starts to move. That is, when the load imposed on the pump motor is large at the portion where the pump motor starts to move, the pump motor cannot start to move, and kept stopped for a predetermined time. Particularly when the pump motor moves immediately after the pressure rises up, the stop problem concerned frequently occurs in accordance with the stop position of the pump motor. Therefore, there is a problem that it takes a time for the pump motor to start its motion or the pump motor is kept stopped and cannot move.
Here, when the pump motor cannot start to move, the pump motor can normally start to move if the voltage/current corresponding to the large load is applied. However, in this case, it is required to mount an expensive pump motor in order to adapt the pump motor to the large load. Furthermore, when application of current/voltage is awaited until a portion to which the current/voltage corresponding to the peak of the load should be applied comes, the phase of the voltage/current applied to the pump motor is displaced. Therefore, the large current/voltage is applied to a portion on which a small load is imposed, and thus the rotational number of the pump motor is varied.
As described above, with respect to the printer, it has been required not only make the pump unit quiet, but also to enable the pump motor to start to move surely.